The present invention relates to grouting pipe equipment for underground water wells and grouting method wherein concrete is cured on the interior wall of a bore hole in order to prevent contaminated surface water and the like from flowing in the water well.
A conventional arrangement for the extraction of groundwater is illustrated in FIG. 1. This arrangement includes:
an outcasing 1, which is installed to prevent the stratum of weathered rock from collapsing into the well. The outcasing 1 is installed following the drilling of the earth from the surface to a bedrock layer with a well drilling machine;
an incasing 3, which is installed to prevent an inflow of surface water. The incasing 3 is installed after installation of the outcasing 1 and subsequent to further drilling of the bedrock layer until a nappe of groundwater is reached;
a strainer pipe 18, which is installed at a position beneath the incasing 3, to allow an influx of groundwater while preventing influx of soil, sand, or other foreign substances;
concrete (not shown), which is injected and cured into the space formed between the incasing 3 and the wall of the water well, to further prevent influx of soil, sand, or other foreign substances;
a water pump 20, which is installed inside the incasing 3;
a water-lifting pipe 22, which is connected to the water pump 20 to lift the groundwater out of the well, and which further includes an upper level sensor 53 and a lower level sensor 54 which enable groundwater to be extracted from the well when the groundwater table is at levels predetermined by the sensors;
a water gauge pole (34), which allows the water table in the well to be monitored at certain depths.
In this conventional arrangement, often the outcasing 1 is too shallow, ending for example at around the middle of the weathered rock layer, when it should be embedded into the bedrock layer. Indeed, sometimes bores have been intentionally formed on the outcasing to allow surface water to flow into the well. Furthermore, synthetic resin incasings are sometimes not installed in a given water well, or if installed, are not grouted. Accordingly, prior art approaches have allowed polluted surface water to flow into groundwater water wells, resulting in pollution of those wells.
Of the above scenarios, a most common problem is the insertion of an incasing without the use of a subsequent grouting process. This often occurred because it was essentially impossible to restrict the depth of the insertion of the incasing, and hence the depth of the concrete.
In another conventional technique for preventing permeation of surface water, a bore hole is drilled to the surface of a bedrock layer, and an outcasing is installed. Thereafter, concrete is injected and cured inside of the outcasing, and then further excavation is performed until a nappe of groundwater is reached, thus forming another bore hole of a smaller diameter to accommodate an incasing. However, this method is inefficient because the grouting process must be performed without knowing the quantity, if any, of the groundwater available at the well site. In other words, the possibility is raised that the well would need to be abandoned as unsuccessful after the expensive process of grouting has been performed.
To solve this particular problem alternative methods have been implemented. Specifically, it has been attempted to drill to the upper layer of a bedrock stratum to insert an outcasing. Then, to accommodate the subsequent placement of an incasing, the drilling bit has been changed to a smaller diameter to allow drilling to continue until a nappe of groundwater is reached. Thereafter, concrete is grouted into the annular space between the incasing and the interior wall of the drilled bore hole to prevent influx of surface water.
This method however is problematic because it is difficult to grout the concrete in the lower portions of the well. Moreover, even if it is possible to grout the lower portions, the groundwater will be contaminated by leakage of the concrete into the well. Furthermore, because the annular space that the concrete fills is typically narrow, for example, about 50-60 mm in width, the concrete may xe2x80x9cbridgexe2x80x9d at some intermediate point in the space and prevent the space from being fully grouted when concrete is introduced from the top of the well. Additionally, if the water table has already risen in the well, the concrete would be diluted by blending with the groundwater present in the annular space, rendering it impossible to cure the concrete to a sufficient strength. To ensure water quality, the grouting process would therefore have to be implemented repeatedly, for example, twice or thrice, resulting in enormous additional construction expenses.
Another alternative approach used in the art has been to drill into the bedrock layer, confirm the presence of groundwater, and then to fill the well with sand from the depth of the nappe to a certain height within the well. Thereafter, lumps of clay or wooden boards are placed on the sand to seal the groundwater, and concrete is then grouted. Excavation can then be continued by removing and discharging the clay, the wooden boards, and the sand until the water is again reached, and then an incasing is inserted.
This approach too suffers from problems. If the central axis of the incasing does not coincide with the shaft of the pre-drilled bore hole, it will be impossible to use. Furthermore, if the sealing materials do not adequately seal of the groundwater, concrete may be injected even into the nappe, and may even cut the nappe off. Hence, the quality and quantity of attainable water is considerably decreased.
In addition to these problems encountered in the prior art, conventional methods suffer from the fact that when a bore hole is drilled, the bore hole may be curved to some extent because of the different constituents of the bedrock layer. In other words, the central axis of the bore hole will not be straight, making insertion of the incasing difficult or impossible, thus resulting in inferior grouting. Additionally, the concrete in conventional methods may infiltrate the nappe, thus either contaminating the water or reducing its quantity. This results because the dependability of the cutoff or sealing means cannot be adequately secured to protect the nappe from the concrete.
Also, these prior art approaches generally contemplate use with wells of larger diameters, and are therefore of limited utility in making underground water wells to service individual houses in rural villages, farms, and other small-scale constructions, which generally are less than 50 mm in diameter. The problems of the prior art are exacerbated for wells of such small sizes.
The disclosed embodiments of the invention provide grouting pipe equipment and easy and efficient grouting methods suitable for use in underground water wells. The various embodiments accomplish this result by better centering the grouting equipment within a bore hole, even in curved bore holes, in an manner that prevents leakage of the grout into the well. Improved grouting is achieved by using corrugated, bendable incasings and expandable tubes which create a seal between the incasing and the well wall for the grout, and which prevent both contaminated surface water and grout from contaminating the groundwater. The disclosed techniques are implementable in such a manner that grouting does not necessarily need to precede the location of a groundwater nappe.